In many applications an axial piston hydraulic pump driven by an electric motor will be utilized to drive a hydraulic device such as a motor or cylinder to operate a machine. A machine such as a press or a shear will be utilized to crush a can, cut a piece of metal or otherwise process a workpiece. Such machines typically operate in two different modes. In the first mode the hydraulic driving motor would be operated at a relatively high speed to move the compression ram or cutting jaws into contact with a workpiece. In the second mode the ram or jaws contact the workpiece and the hydraulic driving motor speed would decrease as the system pressure increases and the motor reaches a set maximum power output.
In the first mode the fluid output of the hydraulic pump to the hydraulic motor initially would have a relatively high flow rate and be at relatively low pressure. During the second mode when the machine demands full power and fluid pressure increases the displacement of the pump would be reduced proportionally to maintain a constant power output.
In some instances the hydraulic system may demand more power than the electric motor is capable of delivering. When this occurs the electric motor becomes overloaded. If an electric motor operates in an overloaded condition for an extended period of time it may experience a premature failure. Consequently, it becomes desirable to automatically adjust the high and low flow rates of the working pressure fluid and to limit the power output from a hydraulic pump when it is driving a working device.
Pump horsepower may be determined by multiplying a constant by the flow rate and the pressure of the working fluid output by the pump. Some previous devices have attempted to maintain a constant horsepower output of a pump by mechanically linking the displacement control of the pump with a device which sets the maximum outlet pressure for the pump. These devices suffer from the disadvantage that pump power cannot be controlled by monitoring system flow at a location remote from the pump.
Thus, it becomes desirable to provide a power limiter control for a variable displacement axial piston pump which maintains a constant power output of the pump by monitoring system flow without regard to the setting of the displacement control for the pump.